Celeron vs Pentium

can someone tell me the major differences between a celeron cpu and the pentium 4 series of processors?
so for example if i was to compare a celeron 2.0 Ghz to a P4 2.0 Ghz whats the differences?
and also any other fats between the two would be helpful, sorry if this has been done over and over, i couldnt find it!
cheers

Celeron has only 128k of L2 cache, whereas the p4's have 512k. This seriously limits the celerons performance compared to a p4 of the same speed. The celerons from 2ghz onwards are based on the northwood core the same as the latest p4's, but before that they were based on the willamette (sp?) core. P4's from 1.8 up are northwoods me thinks.